Ultrasonic bubble point sensor for petroleum fluids in remote and hostile environments

The bubble point is one of the most important physical properties of petroleum fluids. Present practice requires the shipment of samples to laboratories, a time-consuming process that compromises sample integrity. We have devised a method by which the bubble point can be estimated rapidly in a 5 mm diameter flow line immediately after a sample has been withdrawn from a subsurface rock formation. To measure the bubble point, the sample is isolated and depressurized. Measurement efficiency requires rapid depressurization, which often causes fluids to supersaturate. However, this problem can be mitigated by cavitation. We have found that it is possible to cavitate fluids at pressures of several megapascals, as long as the fluid is near its bubble point pressure. An ultrasonic transducer is used to simultaneously nucleate and detect bubbles at or near the thermodynamic bubble point. The cavitated bubbles produce fluctuations in the acoustic properties of the fluid that are detected in the near field or resonated volume of a transducer by measuring the fluctuations of the transducer's electrical properties. The variance of electrical properties increases by orders of magnitude in the presence of bubbles. The method has been demonstrated to work over a wide range of temperatures, pressures and fluids.